This invention has priority rights based on Japanese Patent Application No. 4-313006 filed Oct. 28, 1992, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method for molding a hollow body having an internal opening in a portion of the body and being nearly uniform in thickness around the opening. The present invention also relates to a radiator grille having less weight and a better appearance than conventional grilles.
2. Description of the Related Art
As shown in FIG. 17, a radiator grille 9 for a motor vehicle is conventionally molded from resin, and includes frame 90 and an inner portion 91 located inside the frame. It can be seen in FIGS. 17 and 18, that an internal opening 95 is provided in a lower portion 92 of the frame 90 so as to extend in the longitudinal direction of the lower portion 92. The purpose of providing the internal opening 95 in the grille 9 is to reduce the weight thereof and diminish the required quantity of resin to conserve natural resources. To provide the internal opening 95 in the grille 9 in a conventional method, pressurized gas is injected into the molten resin after the resin is injected into the cavity of a molding die. FIGS. 20 and 21 show the steps of the method of providing the internal opening 95 The resin 7 is injected into an opening gate 85 forming part of a cavity 81 of the molding die 8. The pressurized gas is thereafter injected into the molten resin 7 through the gate 85 so that an internal opening 95 is made in the resin, as shown in FIG. 21.
Although it is desirable for the internal opening 95 to be formed in the central part of the lower portion 92 of frame 90 to make the lower portion nearly uniform in thickness around the opening, it is likely that gravity will cause the upper part 95a as shown in FIG. 19, to be made smaller in thickness than the lower part 95b and side part 95c. Thus, the lower portion 92 is made nonuniform in thickness. The upper part 95a is sometimes made to be quite thin especially at the very center of lower portion 92 as shown in FIG. 19 and thus lacks strength. Therefore, the lower portion 92 needs to be made uniformly large in thickness. Such a problem occurs not only in the radiator grille but also in other hollow molded bodies such as the upper portion of a louver cowl.
A first aspect of the present invention is intended to solve the above-mentioned problem.
In addition, another problem exists in conventional radiator grilles. As shown in FIGS. 22 and 23 a conventional radiator grille 109 is secured by bolts 108 at the front of the engine space of a motor vehicle. The grille 109 includes a securing portion 190, an upper portion 191, a lower portion 192, inner portions 193, a lower ornamental portion 194, an upper ornamental portion 195, and side portions 197. The hood 107 of the vehicle is provided over the engine space so that the hood can be opened and closed. Another conventional radiator grille is secured to the central front portion of the hood of the motor vehicle so that the grille is moved up and down as the hood is opened and closed. Since these grilles are made of a die-cast zinc alloy, they are heavy. To eliminate this disadvantage, the radiator grille is made of resin to weigh less. However, a radiator grille made of the resin is not rigid or strong enough to maintain reliable prolonged use.
A second aspect of the present invention is intended to solve the above-mentioned problems.
A third problem will now be addressed. As shown in FIG. 26, a motor vehicle has a radiator grille 209 at the front thereof. The grille 209 is disposed in front of a radiator for cooling the cooling water of the engine of the vehicle, and plays an important role in improving the appearance of the front of the vehicle. The front of the lower portion 293 of the frame of the grille 209 has an ornamentation 298 for improving the appearance of the lower portion. The ornamentation 298 can be any type of design, such as a flowery pattern, characters, symbols or the like. The frame has side portions 291. The grille 209 is molded of a molded resin so as to weigh less. During the molding process, molten resin is injected into the cavity of a molding die. In order to properly transfer the form of the ornamentation molding portion of the cavity to the lower portion 293 of the grille frame, a pressurized gas is injected into the cavity for the lower portion of the frame after the resin is injected into the cavity. As a result, the molten or soft resin in the cavity is pushed by the pressurized gas so that the form of the ornamentation molding portion of the cavity is properly transferred to the lower portion 293 of the grille frame. As shown in FIGS. 27 and 28, the lower portion 293 has a hollow slender part 208 formed where the gas is injected at gate 281. The resin and the gas are sequentially injected into the cavity through the gate 281. A hollow body molding method is thus utilized to properly transfer the form of the ornamentation molding portion of the cavity to the grille 209.
The resin traveling through internal opening 280 of the hollow slender part 208 sometimes occupies too much of opening 280 (e.g. see numeral 285 in FIG. 28) even though pressurized gas is injected so that the opening 280 does not extend far enough. While resin is pushed by the pressurized gas through the internal opening 280 in order to transfer the form of the ornamentation molding portion of the cavity to the front of the lower portion 293 of the frame of the radiator grille 209, if the resin is not pushed by the gas far enough through the opening 280, the form of the ornamental molding portion will not be transferred to the front of the lower portion 293. This causes the lower portion 293 to have a poor appearance. In order for the internal opening 280 to extend far enough through the resin so that the leading end 285 of the opening reaches the furthermost end 250 of the lower portion 293, the injected quantity of the resin must be controlled so that the resin does not occupy too much of the cavity. In other words, the injected quantity of the resin needs to be controlled as it is injected into the part of the cavity for the hollow slender part 208 of the lower portion 293 before the injection of the gas into the resin in the part. However, since the amount of the cavity which is filled with the resin is not monitored as the resin is injected therein, too much resin is likely to be injected, depending on conditions such as the temperature in the hollow slender part 208 and the form thereof. Since the amount of resin which is injected depends upon such conditions and the like, it is difficult to control the injected quantity of the resin at the time of the injection into the cavity. This is problematic as stated above.
In addition, in the case where the leading end 285 of the internal opening 280 does not reach the vicinity of the furthermost end 250 of the lower portion 293, there is a possibility that a sink mark 299 will be made on the outer surface of a portion which does not have an internal opening as shown in FIG. 28. Since the injected gas does not reach the furthermost end 250 of the lower portion 293 and the end portion 250 is not sufficiently subjected to an internal pressure of the gas, a sink mark 299 is generated on the outer surface thereof. This is also problematic as stated above.
A third aspect of the present invention is intended to solve the above-mentioned problems.